The present invention relates to an improved method for stably ion beam depositing (IBD) tribologically robust, diamond-like carbon (xe2x80x9cDLCxe2x80x9d) films and coatings suitable for use as protective overcoat layers for magnetic recording media, e.g., hard disks, and a multi-process station apparatus including at least one ion beam deposition station, the apparatus being adapted for continuous, stable, automated manufacture of magnetic recording media comprising IBD i-C:H DLC protective overcoat layers formed according to the inventive methodology.
A magnetic recording medium, e.g., a hard disk, typically comprises a laminate of several layers, including a non-magnetic substrate, such as of aluminum-magnesium (Al-Mg) alloy or a glass or glass-ceramic composite material, and formed sequentially on each side thereof: a polycrystalline underlayer, typically of chromium (Cr) or Cr-based alloy, a polycrystalline magnetic recording medium layer, e.g., of a cobalt (Co)-based alloy, a hard, abrasion-resistant, protective overcoat layer, typically carbon (C)-based, and a lubricant topcoat layer.
In operation of the magnetic recording medium, the polycrystalline magnetic recording medium layer is locally magnetized by a write transducer, or write head, to record and store information. The write transducer creates a highly concentrated magnetic field which alternates direction based upon the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer, then the grains of the polycrystalline recording medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of magnetization matches the direction of the applied magnetic field. The magnetization of the polycrystalline recording medium can subsequently produce an electrical response in a read transducer, allowing the stored information to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (CSS) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance above the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, thereby allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
As a consequence of the above-described cyclic CSS-type operation, the surface of the disk or medium surface wears off due to the sliding contact if it has insufficient abrasion resistance or lubrication quality, resulting in breakage or damage if the medium surface wears off to a great extent, whereby operation of the disk drive for performing reading and reproducing operations becomes impossible. The protective overcoat layer is formed on the surface of the polycrystalline magnetic recording medium layer so as to protect the latter from friction and like effects due to the above-described sliding action of the magnetic head. Abrasion-resistant, carbon (C)-containing protective coatings have been utilized for this purpose, and are typically formed by sputtering of a carbon (C) target in an argon (Ar) atmosphere. Such amorphous carbon (a-C)-containing protective overcoat layers formed by sputtering have relatively strong graphite-type bonding, and therefore exhibit a low coefficient of friction in atmospheres containing water (H2O) vapor, which characteristic is peculiar to graphite. However, the a-C layers produced in such manner have very low hardness as compared with many ceramic materials such as are employed as slider materials of thin film heads, and thus are likely to suffer from wear due to contact therewith.
In recent years, therefore, carbon-based protective overcoat layers having diamond-like hardness properties (i.e., HV of about 1,000-5,000 kg/mm2) have been developed, and films of diamond-like carbon (DLC) having a high percentage of diamond-type C-C bonding have been utilized. Such DLC films exhibit a high degree of hardness due to their diamond-like sp3 bonding structure, and in addition, exhibit the excellent sliding properties characteristic of carbon, thus affording improved sliding resistance against sliders composed of high hardness materials. Such DLC films are generally obtained by DC or RF magnetron sputtering of a carbon target in a gas atmosphere comprising a mixture of Ar gas and a hydrocarbon gas, e.g., methane (CH4), or hydrogen (H2) gas. The thus-obtained films exhibit DLC properties when a fixed amount of hydrogen is incorporated therein. Incorporation of excessive amounts of hydrogen in the films leads to gradual softening, and thus the hydrogen content of the films must be carefully regulated.
Amorphous, hydrogenated carbon (a-C:H) films obtained by sputtering of carbon targets in an Ar+H2 gas mixture exhibiting diamond-like properties have also been developed for improving the tribological performance of disk drives; however, the electrical insulating properties of such type films lead to undesirable electrical charge build-up or accumulation over time during hard disk operation which can result in contamination, glide noise, etc. In order to solve this problem without sacrifice or diminution of the advantageous mechanical properties of such a-C:H films, attempts have been made to dope or otherwise incorporate nitrogen (N) atoms into the a-C:H films, in view of a substantial decrease in electrical resistivity and optical band gap (EBG) exhibited by such N-doped a-C:H films relative to undoped films. In addition to these hydrogen-containing DLC materials, amorphous as well as crystalline DLC films and coatings comprising compounds of carbon and nitrogen (CNx) have also been developed and evaluated for use as protective overcoat layers for magnetic recording media.
However, the continuous increase in areal recording density of magnetic recording media requires a commensurately lower flying height. Therefore, it would be advantageous to reduce the thickness of the carbon-based protective overcoat layer to below about 100 xc3x85 without incurring adverse consequences. Conventional sputtered a-C:H and a-C:N materials are difficult to uniformly deposit and generally do not function satisfactorily in hard disk applications at thicknesses of about 100 xc3x85 or less. The use of alternative deposition techniques for developing thinner and harder DLC layers having the requisite mechanical and tribological properties has been examined, such as, for example, chemical vapor deposition (CVD), ion beam deposition (IBD), and cathodic arc deposition (CAD) techniques. Of these, the IBD method has demonstrated ability to be utilized for forming hydrogenated ion-beam deposited carbon (IBD i-C:H) films that exhibit superior tribological performance at thicknesses below about 100 xc3x85.
Conventional gridded, or more commonly, gridless, circularly-configured ion beam sources are typically utilized for the deposition of IBD i-C:H films or coatings, such as end-Hall and closed-drift end-Hall sources, and are extensively described in Handbook of Ion Beam Processing Technology, J. J. Cuomo et al, editors, Noyes Publications, Park Ridge, N.J., pp. 40-54, and in U.S. Pat. No. 4,862,032, the entire disclosure of which is incorporated herein by reference. Such type ion beam sources typically operate at pressures below about 1 mTorr in order to minimize the collision of energetic ions forming the ion beam with ambient energy molecules of the background gas, enable formation of an intense, highly ionized plasma, and to obtain carbon films exhibiting optimum material properties, e.g., hardness, absence of defects, etc., for use as protective overcoat layers in hard disk applications. DLC materials in film or coating form can be produced on suitable hard disk substrates located in the path of the ion beam produced by such gridless ion sources by introducing a hydrocarbon gas (CxHy, where x=1-4 and y=2-10), e.g., acetylene (C2H2), into the ion beam exiting the orifice of the ion beam source or by passing the hydrocarbon gas through the source from the rear thereof. However, the ion beam source is typically integrated with sputtering equipment for continuous, automated manufacture of hard disks such as are employed in computers, and, as a consequence, tradeoffs and/or compromises have been made with respect to material properties and ion beam source operating parameters.
More specifically, a typical automated hard disk manufacturing system includes at least one linearly elongated or circularly-shaped main vacuum chamber having a number of process stations serially arranged therein, each dedicated for deposition of a distinct material layer on the hard disk substrate or to an other type of treatment, e.g., etching, cleaning, etc. When such systems are employed for the manufacture of magnetic recording media, e.g., hard disks, each process station typically comprises a sub-chamber maintained under high vacuum conditions, e.g., for sequentially depositing on the hard disk substrate, as by cathode sputtering, a respective one of the various layers comprising the magnetic recording medium. Workpiece (i.e., substrate) handling/transfer means are provided for transferring the substrates, in sequence, from a preceding station to a following station, with substantially distinct atmospheric conditions being maintained within each sub-chamber, depending upon the particular processing performed therein.
As indicated supra, IBD i-C:H protective overcoat layers are superior to sputtered a-C:H protective overcoat layers, particularly when utilized in ultra-thin thicknesses (i.e.,  less than 100 xc3x85) as required for very high recording density media. As a consequence, when such type multi-process station apparatus is utilized for the manufacture of such high recording density magnetic media, an ion beam source, typically a gridless source such as an end-Hall or closed-drift end-Hall source, is located in an additional sub-chamber within the main chamber and operatively connected therewith by suitable disk transfer means. The ion beam source is supplied with hydrocarbon and argon gases for forming the DLC-type IBD i-C:H protective overcoat layer over the sputtered polycrystalline magnetic recording medium layer. During the ion beam deposition stage, the anode-to-ground voltage of the ion beam source is at or below a level at which arcing or other deleterious effects may occur, typically about 80 V for an end-Hall type source. After deposition of the DLC-type IBD i-C:H layer on the disk substrates is complete, the disk is transferred out of the ion beam deposition (IBD) station/sub-chamber and replaced with a fresh, uncoated disk. However, the transient lowering of the pressure in the IBD chamber which occurs during substrate transfer as a result of exposure to the additional pumping capacity of the main vacuum chamber including process stations operating at substantially lower ambient pressures (typically sputtering stations when such multi-process station apparatus are employed for the manufacture of magnetic recording media), may amount to as much as 50% of the pressure level during the IBD phase and must be taken into account. As a consequence of the transiently lowered pressure in the IBD chamber, the anode potential frequently increases well above 80 V, in some instances reaching about 90-100 V, thereby substantially increasing the likelihood of highly undesirable arcing and particle generation within the ion beam generator and associated vacuum chamber. Such arcing can damage the structural components of the ion beam source as well as the power supply. Moreover, arc-generated particles can contaminate the deposited film, resulting in degradation of film quality, and in extreme cases, loss of product. Stable operation of such hybrid type sputtering/ion beam deposition systems for the formation of tribologically robust DLC materials suitable for use as protective coatings in hard disk manufacture therefore requires an operating regime where the anode-to-ground voltage does not undesirably increase to an arc-producing value upon lowering of the pressure in the IBD sub-chamber during substrate (i.e., disk) transfer.
In addition to the above, the conventional multi-process station methodology incurs the further drawbacks of contamination of the other processing stations with hydrocarbon gases leading to degradation in magnetic recording layer properties and excessive accumulation of potentially explosive hydrocarbon gases in the cryopumps employed for evacuating the main vacuum chamber.
Accordingly, there exists a need for an improved method for stably operating a multi-processing station apparatus including an ion beam processing station for forming very thin, high quality, IBD i-C:H and similar DLC-type abrasion-resistant materials for use as protective overcoat layers for high-density magnetic media, which method overcomes the above-described drawbacks and disadvantages associated with the conventional hybrid IBD/sputtering technology, is simple, cost effective, and fully compatible with the productivity and throughput requirements of automated manufacturing technology.
The present invention fully addresses and solves the above-described problems attendant upon the manufacture of ultra-thin, abrasion-resistant protective overcoat layers suitable for use with high-density magnetic recording media, such as are employed in hard drive applications, while maintaining full compatibility with all mechanical and electrical aspects of conventional disk drive technology.
An advantage of the present invention is an improved method for providing continuous, stable operation of an ion beam source comprising at least one process station of a multi-process station apparatus for continuous, automated manufacture of magnetic recording media, which method eliminates undesirable arcing and particle generation within the ion beam source.
Another advantage of the present invention is an improved method for IBD of ultra-thin, i.e.,  less than 100 xc3x85 thick, tribologically robust i-C:H and similar type DLC coatings suitable for use as protective overcoat layers for high-density magnetic recording media.
Still another advantage of the present invention is an improved, stable-operating, multi-process station apparatus suitable for use in the continuous, automated manufacturing of magnetic recording media and comprising at least one ion beam processing station.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of stably operating an ion beam processing station for treating at least one workpiece therein, the ion beam processing station comprising an ion beam source located within a sub-chamber forming part of a multi-process station apparatus including a main chamber, which method comprises the sequential steps of:
(a) supplying the ion beam source with a flow of at least one inert gas to generate therefrom a first ion beam comprising ions of the at least one inert gas;
(b) providing at least one workpiece within the ion beam processing station;
(c) initiating a flow of at least one reactant source gas to the ion beam source in addition to the flow of the at least one inert gas to generate therefrom a second ion beam comprising ions derived from the at least one reactant source gas;
(d) treating the at least one workpiece with the second ion beam for a preselected interval;
(e) terminating the flow of the at least one reactant source gas to the ion beam source after completion of the preselected interval; and
(f) removing the at least one workpiece from the ion beam processing station and repeating steps (a)-(f) with a fresh workpiece, as desired;
wherein all operating parameters of the ion beam source except for the flow of the at least one reactant gas only during step (c) and the pressure within the sub-chamber are maintained substantially constant during steps (a)-(f).
According to embodiments of the present invention, the method further comprises maintaining at least a preselected minimum pressure within the sub-chamber during steps (a)-(f), thereby eliminating, or at least substantially reducing, arcing and/or particle formation within the ion beam source.
According to further embodiments of the present invention, step (b) comprises providing within the ion beam processing station at least one workpiece comprising a substrate for a magnetic recording medium and including a surface with a plurality of layers formed thereover, the method further comprising depositing the plurality of layers over the substrate surface in the multi-processing station apparatus, the plurality of layers including at least one layer of magnetic recording material having an exposed upper surface; step (c) comprises initiating a flow of hydrocarbon gas of formula CxHy, where x=1-4 and y=2-10, to the ion beam source to generate therefrom a second ion beam comprising C, H, and inert gas-containing ions; and step (d) comprises treating the substrate by directing the second ion beam onto the exposed upper surface of the at least one layer of magnetic recording material to deposit thereon an abrasion-resistant, DLC-type protective overcoat layer of IBD i-C:H.
According to further embodiments of the present invention, step (a) comprises supplying the ion beam source with a flow of argon (Ar) gas as the at least one inert gas to generate the first ion beam therefrom; step (c) comprises initiating a flow of acetylene (C2H2) gas to the ion beam source as the hydrocarbon gas to generate the second ion beam therefrom; and step (d) comprises depositing a layer of IBD i-C:H up to about 100 xc3x85 thick on the exposed surface of the at least one layer of magnetic recording material.
According to particular embodiments of the present invention, the ion source comprises a gridless, circularly-shaped, closed-drift, end-Hall ion source; step (a) comprises generating the first ion beam from the ion source under the following operating conditions:
argon gas flow: about 20 to about 50 sccm
anode current: about 4 to about 12 amperes
anode voltage: about 80 volts
magnet current: about 2 to about 8 amperes
pressure: at least about 0.75 to about 1.0 mTorr
ion energies about 60 to about 100 eV
beam width at substrate: about 4 to about 6 inches diameter;
and step (c) comprises further supplying the ion beam source with the hydrocarbon gas at a flow rate of about 15 to about 40 sccm for a preselected interval of about 2 to about 10 seconds to generate the second ion beam therefrom, the pressure within the sub-chamber being at least about 1.5 to about 2.0 mTorr; the method further comprising maintaining a minimum pressure of at least about 0.75 to about 1.0 mTorr within the sub-chamber during steps (a)-(f), thereby eliminating, or at least substantially reducing, arcing and/or particle formation within the ion beam source.
According to yet further embodiments of the present invention, step (d) comprises depositing an IBD i-C:H DLC-type protective overcoat layer up to about 100 xc3x85 thick; step (b) comprises supplying the ion beam deposition station with a non-magnetic hard disk substrate, comprising a material selected from the group consisting of Al-Mg alloys, glass, and glass-ceramic composite materials; the plurality of layers formed on the surface of the disk substrate comprise, in sequence from the surface, a polycrystalline underlayer comprising Cr or a Cr-based alloy, and a polycrystalline magnetic recording medium layer comprising a Co-based alloy; and the method further comprises step (g) of depositing a lubricant topcoat over the IBD i-C:H protective overcoat layer.
According to another aspect of the present invention, a method of stably operating an ion beam processing station for forming a layer of an abrasion-resistant, DLC-type protective overcoat material on a substrate positioned therein, the ion beam processing station comprising an ion beam source located within a sub-chamber forming part of a multi-process station apparatus including a main chamber, which method comprises the sequential steps of:
(a) supplying the ion beam source with a flow of at least one inert gas to generate therefrom a first ion beam comprising ions of the at least one inert gas;
(b) positioning within the ion beam processing station at least one workpiece comprising a substrate including a deposition surface;
(c) supplying the ion beam source with a flow of a hydrocarbon gas in addition to the flow of the inert gas to generate therefrom a second ion beam comprising C, H, and inert gas ions;
(d) directing the second ion beam onto the surface of the substrate for a preselected interval to deposit a layer of IBD i-C:H thereon;
(e) terminating the flow of hydrocarbon gas after completion of the preselected interval; and
(f) removing the workpiece having the layer of IBD i-C:H deposited thereon and repeating steps (a)-(f) with a fresh workpiece, as desired;
wherein all operating parameters of the ion beam source except for the flow of hydrocarbon gas only during step (c) and the pressure within the sub-chamber are maintained substantially constant during steps (a)-(f).
According to embodiments of the present invention, the ion beam source comprises a gridless, circularly-shaped, closed-drift, end-Hall ion beam source;
step (a) comprises generating the first ion beam under the following operating conditions:
argon gas flow: about 20 to about 50 sccm
anode current: about 4 to about 12 amperes
anode voltage: about 80 volts
magnet current: about 2 to about 8 amperes
pressure: at least about 0.75 to about 1.0 mTorr
ion energies: about 60 to about 100 eV
beam width at substrate: about 4 to about 6 inches diameter;
step (b) comprises positioning within the ion beam processing station a magnetic disk substrate as the workpiece, the magnetic disk substrate comprising a plurality of layers formed over a surface of the substrate, the plurality of layers including at least one layer of a magnetic recording material having an exposed upper surface;
step (c) comprises further supplying the ion beam source with acetylene (C2H2) gas at a flow rate of about 15 to about 40 sccm for an interval of about 2 to about 10 seconds to generate the second ion beam therefrom at a pressure within the sub-chamber of at least about 1.5 to about 2.0 mTorr; and
step (d) comprises depositing a layer of IBD i-C:H up to about 100 xc3x85 thick.
According to still another aspect of the present invention, an apparatus comprises a main vacuum chamber having therein a plurality of sub-chambers defining a plurality of workpiece processing stations, at least one of the plurality of processing stations being an ion beam processing station comprising an ion beam source, gas supply means, and means for transferring workpieces into and out of the at least one ion beam processing station; and
means for stably operating the ion beam source during ion beam processing of the workpiece and during workpiece transfer.
According to embodiments of the present invention, the ion source comprises a gridless, circularly-shaped end-Hall source or a closed drift end-Hall source; and the plurality of workpiece processing stations are linearly or circularly arranged.
Additional advantages of the present invention will become readily apparent to those skilled in the art from the following description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the description is to be regarded as illustrative in nature, and not as limitative.